Method and apparatus for a high-speed search of an optical medium

ABSTRACT

An apparatus and method for high-speed searching of an optical medium having a plurality of tracks. Light spots are directed by the apparatus onto the optical medium. As the spots traverse across the tracks in one of a first direction and a second direction, a photodetector unit receives reflected components of the light spots, thus forming respective electrical signals. Digital shaping circuitry converts the electrical signals into digital signals. A quadrature detector receives the digital signals which are arranged in quadrature relationship to each other, and produces an up-count signal indicating the light spots are traversing the tracks in the first direction and a down-count signal indicating the light spots are traversing the tracks in the second direction. A counter counts the up-count signal and the down-count signal to determine a number of tracks traversed by the light spots.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of “Method and Apparatus for aHigh-Speed Search of an Optical Medium” filed on Jun. 20, 2000 as U.S.patent application Ser. No. 09/597,941, which is incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

[0002] This invention relates generally to a system for recording and/orreproducing digital information on an optical medium, and, moreparticularly, to a system which performs a high-speed search for theinformation stored on the optical medium.

BACKGROUND OF THE INVENTION

[0003] Information is generally stored by an optical disc in the form ofconcentric or spiral tracks sometimes referred to as information tracks.A recording and/or reproducing device rotates the optical disc whileusing a light beam to retrieve the information from or record theinformation to the optical disc. As the optical disc rotates, the lightbeam radially traverses the optical disc while a tracking servo loop inthe recording and/or reproducing device keeps the beam of light centeredon the information track, or, alternately, the track will become theinformation track in the case of recording information to the opticaldisc.

[0004] A three-beam arrangement is one common arrangement used to supplytracking signals to a tracking servo loop, which is maintaining thelight beam on the current track of the optical disc. In thisarrangement, a laser beam passes through a diffraction grading to form acenter beam and two secondary beams. The center beam is used to read orrecord information on the optical disc and the two secondary beams areused for tracking the current track on which the information is beingread or recorded. The two secondary beams form two spots on oppositesides of a track offset with respect to each other. A photodetectorarray includes a main array of four photodetector sensing the reflectionof the center beam and two individual photodetectors, commonly referredto as the E and F photodetectors, sensing light from the two side beamsreflected off of the optical disc.

[0005] A “search” or “seek” operation is a common operation of arecording and/or reproducing device the purpose of which is to move thelight beams from the current track, i.e., the track wherein the lightbeam is presently positioned, to a target track. During the “search”operation, the recording and/or reproducing device typically searchesfor the target track on the optical disc. Achieving a search operationmay require the light beams to radially move across several informationtracks starting from the current track before the target track is found.Once the target address is found, the optical disc storage device canreturn to its normal mode of retrieving or recording information.

[0006] One method of search is to estimate based on the startinglocation of the light beam and the physical parameters of the movementsystem (e.g., mass of a carriage drive, velocity of movement of anoptical head), where the target track might be located, and to theninitiate commands to move the optical head which controls the lightbeams toward this target track. The optical head is then moved to theestimated track. The estimated track is read to determine if the trackhas been reached. If the target track has been overshot or undershot afurther estimate is made and the optical head is again moved in adirection toward the target track. These steps are then repeated untilthe target track is reached. The disadvantage of this approach is thatit is slow because each time a track is read a close loop trackingoperation must be achieved.

[0007] Another method of search is to employ a counter that keeps anaccumulated total of the number of tracks crossed as the optical head ismoved radially across the disc. The optical head then moves towards thetarget track a number of tracks determined to be the absolute value ofthe starting track number subtracted from the target track number. Thisapproach speeds up the search but it is only as effective as theaccuracy of the track crossing counter. Previous counting devices havecounted the total number of tracks traversed whether a track istraversed in a forward or backward direction. In the situation where anoptical disc is subject to vibrations and accleration forces, theoptical head may move back and forward several times from the initialtrack to the destination track. Thus, the total number of tracks countedwill be an overestimate of the actual number of tracks traversed. Anadditional source of error in the count may be introduced due toeccentricity of the optical disc. An inaccurate count track slows downthe search, since if the target track has been overestimated orunderestimated a new search must be initiated in order to move theoptical head to the target track.

[0008] In order to solve the above problems, it is desirable to find anapparatus and method for counting tracks during a search, which isaccurate even in the presence of vibration, acceleration forces,eccentricity, and other sources of error.

OBJECTS OF THE INVENTION

[0009] In view of the foregoing, an object of the present invention isto provide an optical information recording/reproducing apparatus thatis capable of searching a target track with an enhanced reliability.

[0010] Accordingly, another object of the present invention is toprovide an optical information recording/reproducing apparatus which iscapable of searching a target track with an enhanced reliability andaccuracy during a search regardless of the presence of vibrations orother acceleration forces acting on the recording/reproducing apparatus

[0011] Accordingly, another object of the present invention is toprovide an optical information recording/reproducing apparatus that iscapable of a high-speed search.

[0012] It is another object of the present invention to provide ahigh-speed search having improved accuracy of track counting during thehigh-speed search.

[0013] It is yet another object of the present invention to provide asearch apparatus and method with improved accuracy of track countingduring a high-speed search by taking into account the direction ofcrossing of a track during the search.

[0014] It is still another object of the present invention to provide asearch apparatus and method with improved accuracy of track countingduring a high-speed search by counting the net track movement, ratherthan counting the total accumulated movement resulting frombi-directional track crossings.

[0015] It is yet another object of the present invention to provide asearch apparatus and method with improved accuracy of track countingduring a high-speed search by arranging the E and F beams of athree-beam tracking system in quadrature, to thus enable a high-speedsearch based on an accurate track count using simplified components.

[0016] It is still another object of the present invention to provide ahigh-speed search by using a plurality of rates of motion.

[0017] It is yet another object of the present invention to provide ahigh-speed search by using a plurality of rates of motion and choosingone of the rates of motion based on an improved track count of thepresent invention.

[0018] Further objects and advantages of the present invention willbecome apparent from a consideration of the drawings and ensuingdescription.

SUMMARY OF INVENTION

[0019] In order to achieve the above-mentioned objectives, the presentinvention conducts a high-speed search on an optical medium having aplurality of tracks on which information is recorded. At least a firstlight spot and a second light spot are directed by an optical systemonto the optical medium. The light spots traverse across the tracks inone of a first direction and a second direction. A photodetector unitreceives a reflected component of the first light spot and a reflectedcomponent of the second light spot to form, respectively, a firstelectrical signal and a second electrical signal. Digital shapingcircuitry respectively converts the first electrical signal and thesecond electrical signal into a first digital signal and a seconddigital signal. A quadrature detector receives the first digital signaland the second digital signal to produce from the first digital signaland the second digital signal an up-count signal indicating that thelight spots are traversing the tracks in the first direction and adown-count signal indicating that the light spots are traversing thetracks in the second direction.

[0020] According to another aspect of the present invention, a countercounts, during the search, the up-count signal and the down-count signalto determine a number of tracks traversed by the light spots.

[0021] In yet another aspect of the present invention, a micro-computeris coupled to the quadrature detector and is configured to count, duringthe search, the up-count signal and the down-count signal to identify anumber of tracks traversed by the light spots.

[0022] In an additional aspect of the present invention, the first lightspot and the second light spot are arranged on the tracks in aquadrature relationship to each other. In an additional embodiment ofthe present invention, the first electrical signal and the secondelectrical signal are arranged on the tracks in a quadraturerelationship to each other. In another embodiment of the presentinvention, the first digital signal and the second digital signal arearranged in a quadrature relationship to each other.

[0023] In a further aspect of the present invention, the quadraturerelationship is characterized by about a 90-degree shift between thefirst digital signal and the second digital signal.

[0024] In accordance with yet another aspect of the present invention,the quadrature relationship is characterized by a tolerance relationshipbetween the first digital signal and the second digital signal. Thetolerance relationship is determined so that the first digital signaland the second digital signal vary within a specified number of degreesof 90 degrees as permitted by a tolerance parameter of the quadraturedetector.

[0025] In still another aspect of the present invention, the quadraturerelationship is characterized by the first digital signal leading thesecond digital signal in time.

[0026] In yet another aspect of the present invention, the quadraturerelationship is characterized by the second digital signal leading thefirst digital signal in time.

[0027] In accordance with another aspect of the present invention, alight source creates a light beam. A diffraction grating splits thelight beam into at least at least a first light beam and a second lightbeam causing, respectively, the first light spot and the second lightspot. Typically, the quadrature relationship is produced by adjustingthe diffraction grating.

[0028] In still another aspect of the present invention, thephotodetector unit forms a three-beam system comprising a firstphotodetector receiving the first light spot and a second photodetectorreceiving the second light spot.

[0029] In yet another aspect of the present invention, the photodetectorunit forms a three-beam system and a first photodetector receives thefirst electrical signal being an E signal of the three-beam system and asecond photodetector receives the second electrical signal being an Fsignal of the three-beam system.

[0030] In a further aspect of the present invention, a carriage moves aportion of the optical system across the optical medium. The carriagemoves the optical system using one or more rates of motion. Each of theone or more rates of motion is determined to operate within an intervaldefining a distance between tracks of the optical medium. A firstdistance is computed to be a difference between a current track overwhich the optical system is presently positioned and a target track. Thecurrent track is determined from the up-count signal and the down-countsignal. The optical system is moved at the rate of motion correspondingto the interval in which the first distance falls.

[0031] In an additional aspect of the present invention, the quadraturedetector further comprises a first flip-flop having a clock input and aQ output. The first digital signal is coupled to the clock input of thefirst flip-flop. The up-count signal is coupled to the Q output of thefirst flip-flop. A second flip-flop has a clock input and a Q output.The second digital signal is coupled to the clock input of the secondflip-flop. The up-count signal is coupled to the Q output of the secondflip-flop.

[0032] In yet another aspect of the present invention, the digitalshaping circuitry comprises a first Schmitt-trigger which converts thefirst electrical signal into the first digital signal and a secondSchmitt-trigger which converts the second electrical signal into thesecond digital signal.

[0033] In still another aspect of the present invention, the opticalsystem comprises an objective lens which directs the first light spotand the second light spot onto the optical medium.

[0034] In one embodiment of the present invention, a method conducts ahigh-speed search by adjusting at least a first light spot and a secondlight spot to form a quadrature relationship to each other. The firstand second light spots are then directed onto an optical medium. Thelight spots traverse across tracks of the optical medium in one of aninward direction and an outward direction. A reflected component of thefirst light spot is received to form a first electrical signal and areflected component of the second light spot is received to form asecond electrical signal. The first electrical signal and the secondelectrical signal are shaped into a first digital signal and a seconddigital signal. From the quadrature relationship of the first digitalsignal and the second digital signal, an up-count signal indicating thatthe light spots are traversing the tracks in the first direction and adown-count signal indicating that the light spots are traversing thetracks in the second direction are determined.

[0035] In a further aspect of the present invention, the up-count signaland the down-count signal are counted to estimate a number of trackstraversed by the light spots.

[0036] In still another aspect of the present invention, a counter,having sufficient memory to record a maximum number of tracks traversed,receives the up-count signal and the down-count signals and generatesthe estimate of the number of tracks traversed.

[0037] In yet another aspect of the present invention, a micro-computerreceives the up-count signal and the down-count signals and generatesthe estimate of the number of tracks traversed.

[0038] In another aspect of the present invention, the first light spotand the second light spot are moved at one of three rates of movement.One of the three rates of movement is selected based on a distancebetween a current track and a target track wherein the current track isestimated by the counting step.

[0039] In still another aspect of the present invention, a distancebetween a current track over which an optical system is presentlypositioned and a target track is determined. The optical system isconfigured to position the first and the second light spots on theoptical medium. The optical system is moved at a high rate of movementif the distance is greater than a significant distance. The opticalsystem is moved at a medium rate of movement if the distance is greaterthan a nominal distance but less than the significant distance. Themedium rate of movement is less than the high rate of movement. Thenominal distance is less than the significant distance. The opticalsystem is moved at a low rate of movement if the distance is less thanthe nominal distance but greater than a minimal distance. The low rateof movement is less than the medium rate of movement and the minimaldistance being less than the nominal distance. The number of trackscrossed is counted, based on the up-count signal and the down-countsignal, while the optical system is moving according to one of the abovemoving steps, to determine the current track.

[0040] In yet another aspect of the present invention, a methoddetermines a distance between a current track over which an opticalsystem is presently positioned and a target track. The optical system isconfigured to position the first and the second light spots on theoptical medium. A plurality of rates of motion is then determined formoving the optical system. A plurality of disjoint intervals defining anumber of tracks to be crossed is determined. Each one of the pluralityof rates of motion corresponds to one of the disjoint intervals. Theoptical system moves at one of the rates of motion if the distance fallswithin the corresponding interval. The number of tracks crossed iscounted to determine the current track, based on the up-count signal andthe down-count signal, while the optical system is moving according toone of the above moving steps.

BRIEF DESCRIPTION OF DRAWINGS

[0041] In order to facilitate a fuller understanding of the presentinvention, reference is now made to the appended drawings. Thesedrawings should not be construed as limiting the present invention, butare intended to be exemplary only.

[0042]FIG. 1 is a simplified schematic of a recording/reproducingapparatus for recording to and/or reproducing from an optical medium.

[0043]FIG. 2 is a block diagram showing optical elements of therecording/reproduction apparatus according to the present invention.

[0044]FIG. 3 is a diagram showing tracks of an optical recording mediumused in the recording/reproduction apparatus according to the presentinvention.

[0045]FIG. 4 is a diagram showing three beams of a three-beam trackingsystem.

[0046]FIG. 5 is a diagram showing a photodetector array employed in athree-beam tracking system.

[0047]FIG. 6 is a diagram showing circuitry for controlling theread/record beams of the recording/reproduction apparatus according tothe present invention.

[0048]FIG. 7 is a block diagram showing a track crossing detection unitaccording to the present invention.

[0049]FIG. 8 is a diagram of an embodiment of a quadrature detector.

[0050]FIG. 9 shows the electrical signals at selected locations of thetrack crossing detection unit according to the present invention.

[0051]FIG. 10A illustrates the E and F quadrature signals, with the Esignal leading the F signal.

[0052]FIG. 10B illustrates the E and F quadrature signals, with the Fsignal leading the E signal.

[0053]FIG. 11 shows the electrical signals at the input and out-put ofthe quadrature detector according to the present invention.

[0054]FIG. 12 illustrates the main variables of a multi-rate searchaccording to the present invention.

[0055]FIG. 13 is a flow diagram of a method of searching according tothe present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0056] Referring to FIG. 1, there is shown a simplified schematic of arecording/reproducing apparatus 1 for recording to and/or reproducingfrom an information media such as videodiscs, magneto-optical discs,audio discs, and computer data discs, collectively referred to herein asan “optical disc”. Although the following embodiment is described asacting on an optical disc, modifications of the embodiment may also acton other forms of optical media, such as optical tape.

[0057] The recording/reproducing apparatus 1 comprises an optical system10, alternately known in the art as an optical head, for focusing aread/record beam 16 onto and receiving a reflected read/record beam 17from an information-bearing surface 61 of an optical disc 60. In variousembodiments of the recording/reproducing apparatus 1, the read/recordbeams 16 and the reflected read/record beam 17 may be configured toread, record, or to both read and record information to or from theinformation-bearing surface 61 of the optical disc 60. Therecording/reproducing apparatus 1 further comprises a control unit 100for moving the read/record beam 16 with respect to theinformation-bearing surface 61 using the control signals 66, 69, and 72.The control unit 100 receives feed-back in the form of tracking andfocusing information from electrical signals 41 a-f which are receivedfrom the optical system 10, as will be further described below.

[0058] Referring to FIG. 2, there is shown the optical system 10including a light source 15, preferably a laser, employed for generatingthe read/record beam 16 which is used for reading or recording anencoded signal stored on the information formation-bearing surface 61 ofthe optical disc 60. The read/record beam 16 follows a path through afirst lens 20, a diffraction grating 25, a beam splitting prism 30, aquarter wave plate 35, a mirror 36, and an objective lens 38 to a pointof impingement 37 on the information-bearing surface 61 of the opticaldisc 60. The read/record beam 16 is reflected at the point ofimpingement 37 from the information-bearing surface 61 of the opticaldisc 60 to form the reflected read/record beam 17 which follows a returnpath through the objective lens 38, the mirror 36, the quarter waveplate 35, the beam splitting prism 30 to a photodetector unit 40. Thephotodetector unit 40 performs the operation of measuring the intensityof light of the reflected read/record beam 17 and converting thisintensity of light into the electrical signals 41 a-f which are passedto the control unit 100.

[0059] Referring to FIG. 2, the operation of the optical system 10 isnow described in more detail. FIG. 2 shows the read/ record beam 16generated by the light source 15 first passing through the first lens20, which is employed for shaping the read/record beam 16. After theread/record beam 16 is properly shaped by the first lens 20, it passesthrough the diffraction grating 25 which splits the read/ record beam 16into three separate beams 16 a, 16 b and 16 c as shown in FIG. 4.

[0060] The side beams 16 b and 16 c are employed for developing a radialtracking error signal 51 (see FIG. 6) and the center beam 16 a is usedfor developing both a focus error signal 52 (see FIG. 6) and aninformation signal (not shown). The beams 16 a, 16 b, 16 c are treatedidentically by the remaining portion of the optical system 10.Therefore, they are collectively referred to as the read/record beam 16.

[0061] The output of the diffraction grating 25 is applied to the beamsplitting prism 30. The transmitted portion of the read/record beam 16is applied through the quarter wave plate 35 which provides a forty-fivedegree shift in polarization of the light forming the read/record beam16. The read/record beam 16 next impinges upon the mirror 36, whichredirects the read/record beam 16 to the objective lens 38. Theobjective lens 38 is used to shape the read/record beam 16 into a spotof light having a desired size at the point of impingement 37 at whichthe read/record beam 16 impinges upon the information-bearing surface 61of the optical disc 60.

[0062] Referring to FIG. 3, there is shown an enlarged portion of theinformation-bearing surface 61 of the optical disc 60. The optical disc60 includes a plurality of information tracks 73 formed on theinformation-bearing surface 61 of the optical disc 60. Each of theinformation tracks 73 comprises a succession of light reflective regions76 and light non-reflective regions 75. The light reflective regions 76have generally planar, highly polished surfaces, such as a thin aluminumlayer. The light non-reflective regions 75 are generally lightscattering surfaces and appear as bumps or elevations above the planarsurface representing the light reflective regions 76. The read/recordbeam 16 has one or more degrees of movement with respect to theinformation-bearing surface 61 of the optical disc 60, one of which isin the radial direction. The light beam sports 16 a′, 16 b′, 16 c′ areformed by focusing the read/record beams 16 a, 16 b, 16 c onto thetracks 73 of the information-bearing surface 61 of the optical disc 60.The light spots 16 a′, 16 b′, 16 c′ pass over the light reflectiveregions 76 and the light non-reflective regions 75 of the rapidlyrotating the optical disc 60 to form, respectively, the reflectedread/record beams 17 a, 17 b, 17 c, collectively referred to as thereflected read/record beam 17. The three light beam spots 16 a′, 16 b′,16 c′ are positioned on the tracks 73 of the optical disc 60. Data isencoded on the tracks 73 of the optical disc 60 in the form of pits(e.g., 75) and the spaces therebetween 76. If light strikes the spaces76 between the pits 75 it is reflected back into the objective lens 38.If light strikes the pit 75, it is not reflected.

[0063] Referring back to FIG. 2, the reflected light from the point ofimpingement 37 of the optical disc 60 is gathered by the objective lens38 to create the reflected read/record beam 17. The reflectedread/record beam 17 retraces the same path previously explained byimpinging in sequence upon the mirror 36, and the quarterwave plate 35,which provides an additional forty five degree polarization shiftresulting in a cumulative total of one hundred eighty degrees in shiftof polarization. The reflected read/record beam 17 then impinges uponthe beam splitting prism 30 which diverts a portion of the reflectedread/record beam 17 to impinge upon the photodetector unit 40.

[0064]FIG. 5 shows further elements of the photodetector unit 40. Thephotodetector unit 40 is configured as a three-sport tracking pickuparrangement comprising four adjacent photodetectors 40 a, 40 b, 40 c, 40d. Diagonally opposite the larger square comprising the fourphotodetectors 40 a-d are the two tracking photodetectors 40 e, 40 f.The photodetector unit 40 receives the reflected read/record beam 17comprising the reflected read/record beams 17 a, 17 b, 17 c. Thereflected read/record beams 17 a, 17 b, 17 c result from the reflectionof read/record beams 16 a, 16 b, and 16 c from the information-bearingsurface 61 of the optical disc 60. The reflected beams 17 b, 17 cimpinge upon the tracking photodetectors 40 e and 40 f. The center beam17 a impinges on the four adjacent photodetectors 40 a, 40 b, 40 c, 40d.

[0065] Referring back to FIG. 2, the recording/reproducing apparatus 1further comprises mechanisms for moving optical components of theoptical system 10, including a carriage 65, an actuator coil 68, and anactuator coil 71. The carriage 65 radially moves the optical system 10across the information-bearing surface 61 of the optical disc 60 inresponse to the carriage drive signal 66. The actuator coil 68 moves theobjective lens 38 in a direction along a focal plane with respect to theoptical disc 60 in response to the focus drive signal 69. The actuatorcoil 71 moves the objective lens 38 in a radial direction across theoptical disc 60. The tracking drive signal 72 varies a current flowingthrough the actuator coil 71 in a manner that effects a motion of theobjective lens 38 in the radial inward direction 22 a or the radialoutward direction 22 b for tracking. The above-described mechanisms formoving the optical components will be further described with referenceto FIG. 6.

[0066] Referring to FIG. 6, the control unit 100 controls tracking andfocusing of the light spots 16 a′, 16 b′, 16 c′ at the point ofimpingement 37 of the information-bearing surface 61 of the optical disc60. The control unit 100 comprises a digital signal processor (DSP) 120,a microcomputer 130, a track crossing detection unit 200, a keypad 151and/or a remote control keypad/transmitter 150 a and associatedtherewith a remote control receiver 150 b.

[0067] The DSP 120 receives the electrical signals 41 a-f from thephotodetector elements 40 a-f of the photodetector unit 40 which measurethe light intensity from the reflected read/record beams 17 a-c. The DSP120 then performs analog processing on the received electrical signals41 a-f to produce output signals for controlling the relation of theread/record beam 16 with respect to the information-bearing surface 61of the optical disc 60, including a tracking error signal (Te) 51, afocus error signal (Fe) 52, and a carriage signal 53.

[0068] The focus error signal 52 is amplified by an amplifier 54 toproduce the focus drive signal 69 having sufficient current to drive theactuator coil 68. The DSP 120 forms the focus error signal 52 from thephotodetector signals 41 a-d. The focus drive signal 69 varies thecurrent flowing through the actuator coil 68 in a manner that effects amotion of the objective lens 38 in a focal direction with respect to theinformation-bearing surface 61 of the optical disc 60. An apparatus andmethod for focus control is described in Ceshkovsky (U.S. Pat. No.5,978,331), incorporated herein by reference.

[0069] The tracking error signal 51 is amplified by an amplifier 56 toproduce the tracking drive signal 72 having sufficient current to drivethe actuator coil 71. The tracking drive signal 72 varies the currentflowing through the actuator coil 71 in a manner that effects a motionof the objective lens 38 in a radial inward direction 22 a or a radialoutward direction 22 b for tracking. The tracking error signal 51 isformed by taking the difference between the electrical signals outputfrom the photodetectors 40 e and 40 f. FIG. 3 illustrates the pair oftracking light spots 16 b′ and 16 c′ irradiated so that they form a pairof tracking beams to be disposed symmetrically with the center beamlight spot 16 a′ sandwiched therebetween on a line forming apredetermined angle with respect to the track 73 to which tracking isperformed.

[0070] The reflected light rays of the pair of tracking beams 17 e, 17 ffrom the information-bearing surface 61 of the optical disc 60 arerespectively received by the pair of photodetector 40 e and 40 f. Thedifference between the respective electrical signals 41 e and 41 foutput from the photodetectors 40 e and 40 f is employed as the trackingerror signal 51. An apparatus and method for tracking is described inCeshkovsky (U.S. Pat. No. 5,689,485), incorporated herein by reference.

[0071] The carriage signal 53 is amplified by an amplifier 55 to producethe carriage drive signal 66 having sufficient current to direct thecarriage drive 65 to move the optical system 10 radially across theinformation-bearing surface 61 of the optical disc 60.

[0072] The microcomputer 130 has resident therein programs forcontrolling the recording/reproducing apparatus 1, including programsfor controlling the tracking error signal 51, the focus error signal 52,and the carriage signal 53. The microcomputer 130 is electricallycoupled to the DSP 120 through a serial bus 111 over which informationand control signals are transmitted. The microcomputer 130, preferablydirected by one of the resident programs, directs the point ofimpingement 37 of the read/record beam 16 on the information-bearingsurface 61 of the optical disc 60 so as to radially track theinformation carrying indicia located on the tracks 73 on theinformation-bearing surface 61 of the optical disc 60. The tracking isaccomplished by driving the actuator coil 71 to respond to the trackingerror signal 51, so that the point of impingement 37 of the read/recordbeam 16 is directed to a desired position in a radial direction over theinformation-bearing surface 61 of the optical disc 60.

[0073] A user may initiate commands such as “search” or “pause” to themicrocomputer 130 by entering the commands on a key pad 151 or,alternately, on the remote control key pad 150 a remotely coupled to theremote control receiver 150 b. The microcomputer 130 may have residentone or more computer programs to carry out a search for a track of theinformation-bearing surface 61 of the optical disc 60. The microcomputer130 receives one or more signals from the track crossing detection unit200, including an up-count signal 225, a down-count signal 226, and acounter output signal 227. The microcomputer 130 direct the search bycontrolling the tracking drive signal 72 and/or the carriage drivesignal 66 by issuing commands through the serial bus 111.

[0074]FIG. 7 shows the track crossing detection unit 200 comprising thephotodetectors 40 e, 40 f, pre-amplifiers 215, 216, low pass filters220, 221, pulse shapers 230, 231, a quadrature detector 240, and anup/down counter 250. The track crossing detection unit 200 outputs theup-count signal 225, the down-count signal 226, and the counter outputsignal 227. The signals 225, 226, 227 are electrically coupled as inputsto the microcomputer 130 shown in FIG. 6. The up/down counter 250produces the counter output signal 227 representing a numerical valuedepending on the inputs 225, and 226. A pulse on the up-count signal 225increments by one the counter out-put signal 227. A pulse on thedown-count signal 226 decrements by one the counter output signal 227.

[0075] Referring to FIG. 7, there is shown the photodetectors 40 e and40 f, having received the reflected read/record beams 17 e and 17 f,respectively, converting the reflected read/record beams 17 e and 17 fto electrical signals 41 e and 41 f, respectively. The pre-amplifiers215, 216 amplify the electrical signals 41 e and 41 f, respectively, toform, respectively, the amplified electrical signals 42 e and 42 f. Anexample of the signals 42 e and 42 f is depicted in FIG. 9. The signals42 e, 42 f are shown having high frequency noise resulting fromtraversing the tracks of the information-bearing surface 61 of therapidly rotating the optical disc 60.

[0076] During the search mode light beam spots 16 a′, 16 b′, and 16 c′traverse the information tracks 73 of the information-bearing surface 61of the optical disc 60 in approximately a radial direction. As lightbeam spots 16 a′ and 16 c′ traverse the disc, the electrical signals 41e and 41 f form a sinusoidal like waveform as a result of thedifferences in reflectance between the areas of the tracks containinginformation and the areas not containing information. The electricalsignals 41 e and 41 f have been previously adjusted to form a quadraturerelationship with each other.

[0077] Each of the signals 42 e, 42 f is passed through the respectivelow pass filter 220, 221 to remove any high frequency noise to producefiltered electrical signals 43 e, 43 f as shown in FIG. 9. Each of thefiltered signals 43 e, 43 f passes through one of the respective pulseshaping circuits 230, 231, preferably a Schmitt-trigger, to convert eachsignal to its respective digital signal 44 e, 44 f having square pulseshapes as shown in FIG. 9. The pulse shaping circuits 230, 231 mayinclude other pulse shaping means such as an analog comparator. Thedigital signals 44 e, 44 f are input to the quadrature detector 240.

[0078] The signals 44 e, 44 f are prepared for reception by thequadrature detector 240 by adjustment of the signals 44 e, 44 f to forma quadrature relationship an example of which is depicted in FIG. 9. Aquadrature relationship is formed by adjustment of the light spots 16b′, 16 c′, or by adjustment of one of the electrical signals, includingthe smooth signals 42 e, 42 f, and the digital signals 44 e, 44 f. Thedigital signals 44 e, 44 f are adjusted to form a 90-degreerelationship. Additionally, the digital signals 44 e, 44 f are alsoadjustable to form an approximately 90-degree relationship as permittedby the tolerance requirements the quadrature detector 240. In oneembodiment, the tracking spots 16 b′ and 16 c′ are adjusted by rotatingthe diffraction grating 25 so that the digital signals 44 e and 44 fform a quadrature relationship with each other. However, other methodsof adjusting the signals 44 e and 44 f to form a quadrature relationshipare not precluded, for example, adjusting the positions of the lightsource, objective lens, mirror angle, and/or optical and electricalparameters of the recording/reproducing apparatus 1. Additionally, inother embodiments the quadrature relationship may be established withrespect to other signal pairs, including the light spot pair 16 a′, 16b′, the signal pair 41 e, 41 f, the signal pair 42 e, 42 f, and thesignal pair 43 e, 43 f.

[0079]FIG. 8 shows the quadrature detector 240 comprising a JK flip-flop263 and a JK flip-flop 264. The JK flip-flop 263, comprising a clockinput (CLK), a Q output and a Q-overscore output, receives the signal 44e in the clock in-put (CLK) and outputs the signal 225 from theQ-overscore output. The JK flip-flop 264, comprising a clock input(CLK), a Q output and a Q-overscore output receives the signal 44 f inthe clock input (CLK) and outputs the signal 226 from the Q-overscoreoutput. The Q-overscore output of the JK flip-flop 263 is connected to aJ input of the JK flip-flop 263. The Q-overscore output of the JKflip-flop 264 is connected to a J input of JK flip-flop 264. The Kinputs of the JK flip-flops 263, 264 are connected to each other and toground. The signal 44 e additionally connects to a reset input 265 ofthe JK flip-flop 264. The signal 44 f additionally connects to a resetinput 266 of the JK flip-flop 263. The resets 265, 266 reset on thenegative transition edges.

[0080] In the case when movement of the optical system 10 causesread/record beams 16 a, 16 b, 16 c to radially traversed the tracks ofthe information-bearing surface 61 of the optical disc 60 in an inwarddirection 22 a, i.e., moving from the outer edge of theinformation-bearing surface 61 of the optical disc 60 to the inner edgeof the information-bearing surface 61 of the optical disc 60, light beamspots 16 a′, 16 b′, and 16 c′ radially cross the tracks 73 of theinformation-bearing surface 61 of the optical disc 60 with the reflectedlight beam spot 16 b′ preceding the reflected light spot 16 c′. As aresult, as shown in FIG. 9, the electrical signal 42 e will lead theelectrical signal 42 f as the light beam spot 16 b′ proceeds the lightspot 16 c′ by approximately 90 degrees, the signals 44 e and 44 f havingbeen previously adjusted to be in a quadrature relationship.

[0081] As illustrated in FIG. 9 and repeated in FIG. 10A, traversal ofthe information-bearing surface 61 in the inward direction 22 a causesthe signal 44 e to lead the signal 44 f. As a result, a falling edge 347of the signal 44 e occurs in time before a falling edge 350 of thesignal 44 f. The falling edge 347 of the signal 44 e input to the CLKinput of the JK flip-flop 263 has the effect of setting the Q output ofthe upper JK flip-flop 263 high. The JK flip-flop 263 is reset setasynchronously by a low level 349 on the signal 44 f. Thus, the upper JKflip-flop 263 pulsates with every cycle of tracks traversed. The fallingedge 350 of the signal 44 f, which is input to the clock input of thelower JK flip-flop 264 won't set the Q output of the JK flip-flop 264 toa high level because the Q output of the JK flip-flop 264 is held low bya low level 351 of the signal 44 e, which is fed into the asynchronousreset input 265 of the JK flip-flop 264. Consequently, the Q output ofthe JK flip-flop 264 always stays low, and the Q-overscore output 226always stays high while the light beam spots 16 a′, 16 b′, 16 c′traverse the tracks 73 of the optical disc 60 in the radially inwarddirection 22 a.

[0082] In the case when movement of the optical system 10 causes theread/record beams 16 a, 16 b, 16 c to radially traverse the tracks ofthe optical disc 60 in the radially outward direction 22 b, the lightbeam spots 16 a′, 16 b′, and 16 c′ radially cross the tracks 73 on theinformation-bearing surface 61 of the optical disc 60 with reflectedlight spot 16 c′ preceding reflected light beam spot 16 b′. As a result,as shown in FIG. 10B, the signal 44 f will lead the signal 44 e in timeby approximately 90 degrees, the signals 44 e and 44 f having beenpreviously set to be in a quadrature. When the optical disk is traversedin the radially outward direction 22 b, the signal 44 f leads the signal44 e. Thus, the falling edge 350 of the signal 44 f has the effect ofsetting the Q output of the lower JK flip-flop 264 high. Then the JKflip-flop 264 is reset asynchronously by the low level 351 on the signal44 e. Thus, the lower JK flip-flop 264 pulsates with every cycle oftracks traversed. The falling edge 347 of the signal 44 e, which isinput to the clock input of the upper JK flip-flop 263, won't set the JKflip-flop 263 high. That is because the JK flip-flop 263 is held low bythe low level 349 of the signal 44 f, which is fed into the asynchronousreset input 266 of the JK flip-flop 263. Consequently, the Q output ofthe JK flip-flop 263 always stays low and the Q-overscore output 225always stays high while light beam spots 16 a′, 16 b′, 16 c′ traversesthe tracks 73 of the optical disc 60 in the radially outward direction22 b. FIG. 10A showing signal 44 e leading signal 44 f and is to becontrasted with FIG. 10B showing signal 44 f leading signal 44 e.

[0083]FIG. 11 shows two signals output from the quadrature detector 240,the up-count signal 225 and the down-count signal 226. A pulse on theup-count signal 225 indicates the light spots 16 b′, 16 c′ havetraverses a track of the optical disc 60 radially inwardly 22 a. A pulseon the down-count signal 226 indicates the light spots have traversed atrack of the optical disc 60 in the radially outward direction 22 b.

[0084] The up-count signal 225 and the down-count signal 226 areconnected to the up/down counter 250 that counts in an incremental waythe number of tracks traversed. The up/down counter 250 receives thefirst signal 225 indicating the up-count and the second signal 226indicating the down-count. A pulse on the first signal 225 causes theup/down counter 250 to increment an accumulated total by one. A pulse ofthe second signal 226 causes the up/down counter 250 to decrement theaccumulated total by one. The up/down counter 250 is of sufficient sizeto store the maximum number of tracks to be traversed during the search.Alternately, the up-count signal 225 and the down-count signal 226 maybe connected directly to the microcomputer 130. This requires the use ofinterrupt inputs of a very fast microcomputer.

[0085] The first part (0<t<to, where t is time) of FIG. 11 shows theoutputs 225,226 of the quadrature detector 240 caused by the inputs 44e, 44 f in the case where the search direction is in the radially inwarddirection 22 a so that the signal 44 e leads the signal 44 f by about 90degrees. As a result, the signal 225 pulsates for each track traversalwhile the signal 226 remains high.

[0086] In the second part (t>to) of FIG. 11, the search direction beingreversed to the radially outward direction 22 b causes a phase changeobservable by a pulse 361 of signal 44 f being of shorter duration thanthe other pulses.

[0087] The signal 44 f now leads the signal 44 e by about 90 degrees. Asa result, the signal 226 pulsates for each track traversal while thesignal 225 remains high.

[0088] The present invention has the advantage of improving the accuracyof a high-speed search even in the situation where acceleration forcesare applied to the optical pickup during the high-speed search. Becauseeither an up-pulse or a down-pulse is produced for each track traversed,the optical pickup may move several times back and forth between theinitial track and the target track of the search and the correct numberof tracks traversed will still be counted. This is not true of a devicethat forms a count estimate from an integrated average of trackstraversed during a predetermined time period.

[0089]FIG. 13 shows a method of search 400 typically directed by aprogram resident in the microcomputer 130. The microcomputer 130 isconfigurable to receive the count signal 227 from the up/down counter250 or, alternately, the up-count signal 225 and the down-count signal226 directly from the quadrature detector 240.

[0090] At step 401, the search begins by determining the target trackand the current track. The target track is input by a user via keypads151, 150 a or otherwise determined by a program of the microcomputer130. The current track is initially determinable, for example, byreading a track address imprinted on the current track.

[0091] At step 405, the difference (d) is determined by subtracting thecurrent track location from the target track location. At step 410 if itis decided that the target track location is greater than the currenttrack location (d>0), a forward search is initiated at step 420, or,conversely if the target track location is less than the current tracklocation (d<0), a reverse search is initiated at step 415.

[0092] As illustrated in FIG. 12, one of three rates of movement of theoptical system 10 is initiated based on the relationship of the distancebetween the current and target track. The rates of movement of thecarriage 65 are denoted high, medium, and low wherein low<medium<high.The following distance values are pre-determined: minimal (min), nominal(nom), and significant (sig), wherein min<nom<sig, as illustrated inFIG. 12. The high rate of movement is initiated if the difference indistance between the current track and the target track is more than thesignificant distance (i.e., d>sig). The medium rate of movement isinitiated if the difference between the current track and the targettrack is less than the significant distance but greater than the nominaldistance (i.e., nom<d<sig). The low rate of movement is initiated if thedifference between the current track and the target track is greaterthan a minimum distance but less than the nominal distance (i.e.,min<d<nom). The final search is conducted when the difference is lessthan the minimum distance (i.e., d<min). The three parameters, i.e.,min, nom, sig, and the three velocity parameters, i.e. low rate, mediumrate, high rate, are chosen based on the characteristics of the opticalsystem 10, such as the mass of the carriage 65 and the accelerationforce applied on the carriage 65.

[0093] It is decided at step 425 whether d>sig. If d>sig, then in step430 the microcomputer 130 sends a first signal to the DSP 120 to disablethe track drive signal 72 and sends a second signal to the DSP 120 toactivate the carriage 65 to move the optical system 10 at a high speedin a forward or reverse direction as was decided at step 410.Consequently, the carriage 65 is moved at the high speed in an open-loopmode until a first pre-determined number of tracks have been countedusing the up/down counter 250 to determine the track crossing count. Theoptical system 10 then completes its movement. In step 425, if d <sig,then the method proceeds to step 435.

[0094] It is decided at step 435 if the distance between the currenttrack and the target track is more than the nominal but less than asignificant distance (nom<d<sig). If nom<d<sig, then in step 440 themicrocomputer 130 send a first signal to the DSP 120 to disable thetrack drive signal 72 and a second signal to the DSP 120 to activate thecarriage 65 to move the optical system 10 at the medium speed in aforward or reverse direction as was decided at step 410. Consequently,the carriage 65 is moved at the medium speed in an open-loop mode untila second pre-determined number of tracks have been counted using theup/down counter 250 to determine the track crossing count. The opticalsystem 10 then completes its movement. In step 435, if d<nominal, thenthe method proceeds to step 445.

[0095] It is decided at step 445, if the difference between the currenttrack and the target track is more than a minimal distance but less thana nominal distance (i.e., min<d<nom). If min<d<nom, then at step 450 themicrocomputer 130 sends a first signal to the DSP 120 to disable thetrack drive signal 72 and a second signal to activate the carriage 65 tomove the optical system 10 at a the low speed in a forward or reversedirection as was decided at step 410. Consequently, the carriage 65 ismoved at the low speed in an open-loop mode until a third pre-determinednumber of tracks have been counted using the up/down counter 250 todetermine track crossing count.

[0096] After any on of the above search movements 430, 440, 450 has beencompleted the current track location is re-computer by the microcomputer130 and compared to the target track to determine if further movement isnecessary at step 470 to move the optical system 10 over the targettrack as described above.

[0097] In step 445, if d<minimal, then the method proceeds to step 455.The final search mode at step 455 is the most fine grade search. Thefinal search mode is initiated if the difference between the currenttrack and the target track is less than the minimal distance. The finalsearch is conducted in closed-loop mode and characterized by a series ofindividual track movements in the direction necessary to reach thetarget track. To initiate the final search, the microcomputer 130 sendsa signal to the DSP 120 to enable the track drive signal 72. In theevent that after final search the target location is not located for anyreason the target track is incremented by a predetermined amount and thefinal search mode is re-initiated. At the end of this search, thecorrect track is located and the micro-computer initiates a transfer ofdata at step 460 by reading the data located on the identified track.The effectiveness of the high-speed search method described herein isenhanced by the accurate track counting of the present invention.

[0098] In another embodiment of the present invention, the search method400 is generalized to operate with one or more rates of motion (otherthan 3 as has been described). A plurality of disjoint intervals aredefined similar to what was done in the search method 400 wherein fourintervals were defined (see FIG. 12). Each interval defines an operatingrange for a rate of motion. The optical system 10 moves at one of therates of motion if the distance falls within the corresponding interval.The number of tracks crossed is counted to determine the current track,based on the up-count signal 225 and the down-count signal 226, whilethe optical system 10 is moving according to one of the above movingsteps.

[0099] The present invention is not to be limited in scope by thespecific embodiments described herein. Indeed, this application isintended to cover any modifications of the present invention, inaddition to those described herein, and the present invention is notconfined to the details which have been set forth. Thus, the scope ofthe invention should be determined by the appended claims and theirlegal equivalents, rather than by the examples given.

1. An apparatus for conducting a high speed search on an optical mediumhaving a surface on which information is recorded comprising: aphotodetector unit configured to receive a reflected component of afirst light spot to form a first electrical signal and a reflectedcomponent of a second light spot to form a second electrical signal;digital shaping circuitry configured to respectively convert the firstelectrical signal and the second electrical signal into a first digitalsignal and a second digital signals; and a detector configured toreceive the first digital signal and the second digital signal toproduce from the first digital signal and the second digital signal anup-count signal and a down-count signal indicating directions that thelight spots traverse.
 2. The apparatus of claim 1 wherein the surfaceincludes a plurality of tracks.
 3. The apparatus of claim 2 wherein oneof the first light spot and the second light spot is directed by anoptical system on to the optical medium.
 4. The apparatus of claim 3wherein the up-count signal indicates the first light spot is traversingthe tracks in a first direction and the down-count signal indicates thesecond light spot is traversing the tracks in a second direction.
 5. Theapparatus of claim 4, further comprising: a counter configured to count,during the search, the up-count signal and the down-count signal todetermine a number of tracks traversed by the light spots.
 6. Theapparatus of claim 4, further comprising: a microcomputer coupled to thequadrature detector and configured to count, during the search, theup-count signal and the down-count signal to identify a number of trackstraversed by the light spots.
 7. The apparatus of claim 4, wherein: thefirst light spot and the second light spot are arranged on the tracks ina quadrature relationship to each other.
 8. The apparatus of claim 4,wherein: the first electrical signal and the second electrical signalare arranged on the tracks in a quadrature relationship to each other.9. The apparatus of claim 4, wherein: the first digital signal and thesecond digital signal are arranged in a quadrature relationship to eachother.
 10. The apparatus of claim 9, wherein: the quadraturerelationship is characterized by about a 90-degree shift between thefirst digital signal and the second digital signal.
 11. The apparatus ofclaim 9, wherein: the quadrature relationship is characterized by atolerance relationship between the first digital signal and the seconddigital signal, the tolerance relationship being determined so that thefirst digital signal and the second digital signal vary within aspecified number of degrees of 90 degrees as permitted by a toleranceparameter of the quadrature detector.
 12. The apparatus of claim 9,wherein: the quadrature relationship is characterized by the firstdigital signal leading the second digital signal in time.
 13. A methodfor conducting a high speed search, comprising: directing a first and asecond light spots onto an optical medium, the light spots traversingacross the surface of the optical medium; receiving a reflectedcomponent of the first light spot to form a first electrical signal anda reflected component of the second light spot to form a secondelectrical signal; shaping the first electrical signal and the secondelectrical signal into a first digital signal and a second digitalsignal; and determining from the first digital signal and the seconddigital signal an up-count signal and a down-count signal.
 14. Themethod of claim 13 further comprising directing the first and secondlight spots to form a quadrature relationship to each other.
 15. Themethod of claim 13 wherein the surface comprises a plurality of tracks.16. The method of claim 15 wherein the first and second signalsrespectively indicate the light spots traversing the tracks in a firstand a second direction.
 17. The method of claim 16, further comprising:counting the up-count signal and the down-count signal to estimate anumber of tracks traversed by the light spots.
 18. A method forconducting a high-speed search, comprising: determining a target trackover which an optical system is to be positioned; measuring a currenttrack over which the optical system is currently positioned; determininga distance (d) between the target track and the current track; moving inan open loop mode the optical system at one of a plurality of rates ofmotion until the optical system rests, to each one of the plurality ofrates of motion there being assigned one interval from a plurality ofdisjoint intervals, wherein if d falls within one of the disjointintervals the optical system is moved the corresponding rate of motion;and measuring the current track to recalculate d.
 19. The method ofclaim 18 further comprising repeating the moving step until d issufficiently small.
 20. The method of claim 18 further comprising movingthe optical head one track at a time in a closed loop mode until thetarget track is reached.